1. Field of the Invention
The present invention relates to an ink jet recorder having a purging device for sucking ink from a ink jet head and a purging method therefor.
2. Description of Related Art
Ink jet printers are known generally as ink jet recorders for recording on recording media, such as sheets of paper, by ejecting ink onto them. FIG. 9 of the accompanying drawings shows part of a conventional ink jet printer, which includes a recording head unit P3 having a recording head P2. The head P2 has four ejection nozzles P4, each of which has ejection holes (not shown) opening in its front surface P5. The ejection nozzles eject different colored inks including black, yellow, cyan and magenta, respectively. Four ink cartridges P1 containing the respective colored inks are mounted replaceably on the head unit P3, and each connected to the corresponding nozzle P4. After each cartridge P1 is replaced with a new one, ink is supplied from the new cartridge to the head P2, and can be ejected from the associated nozzle P4.
The printer is provided with a purging device having a cap P6 and a suction pump (not shown) in order to purge the nozzles P4. The purging may be started manually by the user operating a switch on the printer, or automatically if a predetermined condition is satisfied. The purging is performed to prevent the defective ejection of ink which may be caused if the ink in or on the recording head P2 dries, or if air bubbles are produced in the ink, or if droplets of ink stick to the nozzle surfaces P5. The purging is also performed for introducing the ink into the recording head P2 when the ink cartridge P1 is replaced. Specifically, the purging of each nozzle P4 involves covering its nozzle surface P5 with a suction cap P6, and then developing negative pressure in the cap P6 by means of a suction pump (not shown), in order to suck ink from the head P2 through the cap P6 and discharge the sucked ink outside.
Conventionally, when the purging operation is performed for all four ejection nozzles P4, the four ejection nozzles P4 will be successively purged using one suction cap P6. The order in which the nozzles will be subjected to purging is determined by the lightness of the ink for the following reason. For example, when the purging operation is performed on two nozzles, the ink from one nozzle purged earlier may be deposited on the surface of the other nozzle to be purged next by the suction cap P6. In this situation, if the ink color ejected from the other nozzle is darker than that from the earlier purged nozzle, the printed color is little damaged because the darker color ink from the other nozzle might not be affected by the lighter color ink.
However, there has been a problem when the purging operation is performed in such a way that the ejection nozzle for the lighter color ink is purged earlier than the nozzle ejecting the darker ink. When the recording starts immediately after the purging, non-ejection of the darker ink might occur because of the air bubbles remaining in an ink passage after the purging. The non-ejection results in a noticeable lack of color on the printing medium. In order to avoid the problem, a certain waiting time was needed after the completion of purging before the recording could be started, so that the air bubbles in the passage could be absorbed into the ink, and thereby vanish therein.
U.S. patent application Ser. No. 09/053,756 filed on Apr. 2, 1998, which will be assigned to the present Assignee and corresponds to Japanese Patent Application No. 9-85366 filed on Apr. 3, 1997, discloses an ink jet printer provided with a recording head having a plurality of ejection surfaces each containing a nozzle for ejecting a different ink and a purging device for purging the nozzle of one ejection surface at a time. The printer also has a controller for controlling the purging device such that a nozzle having an ink with higher dry resistance is purged before a nozzle having an ink with lower dry resistance. The printer can prevent the nozzles from drying during the purging operation.
U.S. patent application Ser. No. 08/995,516 filed on Dec. 22, 1997, which will be assigned to the present Assignee and corresponds to Japanese Patent Application No. 9-85684 filed on Mar. 19, 1997, discloses an ink jet recorder provided with a plurality of recording heads each having ejection nozzle for ejecting a different color ink, an ink suction device for sucking ink from each head, and a pre-ejecting device for ejecting ink toward a portion for receiving used ink after sucking ink. When the ink is sucked from at least two heads within the plurality of heads, the ink suction device sucks the ink in an order which is different from an order of lightness of the ink color. As the ink for pre-ejection has a lighter color, the pre-ejection device pre-ejects the ink in larger amount.